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.TH SEM_GETVALUE 3C "Feb 5, 2008"
.SH NAME
sem_getvalue \- get the value of a semaphore
.SH SYNOPSIS
.LP
.nf
#include <semaphore.h>

\fBint\fR \fBsem_getvalue\fR(\fBsem_t *restrict\fR \fIsem\fR, \fBint *restrict\fR \fIsval\fR);
.fi

.SH DESCRIPTION
.sp
.LP
The \fBsem_getvalue()\fR function updates the location referenced by the
\fIsval\fR argument to have the value of the semaphore referenced by \fIsem\fR
without affecting the state of the semaphore. The updated value represents an
actual semaphore value that occurred at some unspecified time during the call,
but it need not be the actual value of the semaphore when it is returned to the
calling process.
.sp
.LP
If \fIsem\fR is locked, then the value returned by \fBsem_getvalue()\fR is
either zero or a negative number whose absolute value represents the number of
processes waiting for the semaphore at some unspecified time during the call.
.sp
.LP
The value set in \fIsval\fR may be 0 or positive. If \fIsval\fR is 0, there may
be other processes (or LWPs or threads) waiting for the semaphore; if
\fIsval\fR is positive, no process is waiting.
.SH RETURN VALUES
.sp
.LP
Upon successful completion, \fBsem_getvalue()\fR returns \fB0\fR. Otherwise, it
returns \fB\(mi1\fR and sets \fBerrno\fR to indicate the error.
.SH ERRORS
.sp
.LP
The  \fBsem_getvalue()\fR function will fail if:
.sp
.ne 2
.na
\fB\fBEINVAL\fR \fR
.ad
.RS 11n
The \fIsem\fR argument does not refer to a valid semaphore.
.RE

.sp
.ne 2
.na
\fB\fBENOSYS\fR \fR
.ad
.RS 11n
The \fBsem_getvalue()\fR function is not supported by the system.
.RE

.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Committed
_
MT-Level	MT-Safe
_
Standard	See \fBstandards\fR(7).
.TE

.SH SEE ALSO
.sp
.LP
.BR semctl (2),
.BR semget (2),
.BR semop (2),
.BR sem_post (3C),
.BR sem_wait (3C),
.BR attributes (7),
.BR standards (7)
